Once I was asked, why I do my Punch the way I do. Most often, my Tsuki (Punch) resembles a combination between a vertical and a horizontal punch.
The answer is quite simple, it feels natural.
The best way to explain it is to compare my Tsuki with push-ups!
Yes, you read right, push-ups.
Try taking push-ups on the knuckles. Most people will perform them as shown in the picture below.
That said, it feels natural.